(593m) High Cell Density Cultivation of Azotobacter Vinelandii in Pilot Scale Stirred Tank Bioreactors for Biofertilizer Applications

Then,C¹, ,Othman, N.Z^2, Malek, R.A², , Peng, T¹, Chang, H.W¹, Sukumaran,S¹, Wan Mustapha, W.A¹,Ramli, S², Saat, M², Sarmidi, M.R², Aziz, R², El Enshasy, H.A^2,3

1. All Cosmos Industries Sdn Bhd, Pasir Gudang, Johor Bahru, Malaysia

2. Institute of Bioproduct Development (IBD, Universiti Teknologi Malaysia, (UTM), 81310 UTM Skudai, Johor, Malaysia;

3. Bioprocess Development Departments, City for Scientific Research (CSAT), New Burg Al Arab, Alexandria, Egypt.;

Abstract

Azotobacter vinelandii is a free living N-fixing bacterium capable of converting stable atmospheric nitrogen into ammonia, a nitrogen source easily assimilated by plants. Although, extensive research has been done on the genomics, metabolism, alginate productivity and plant growth promoting capabilities of this strain, there is little data on high cell density cultivations for biofertilizer applications. Therefore, the objective of this work is to study the parameters affecting cell growth in 16-L and 150-L pilot scale stirred tank bioreactors so as to determine the optimum cultivation conditions for cell mass production. Batch cultivation in a 16-L stirred tank bioreactor with and without pH control yielded cell mass concentrations of 7.52 g L^-1 and 15.86 g L^-1 respectively. A series of fed-batch cultivations was subsequently carried out to determine the factors limiting cell growth. A combination of a constant feeding strategy coupled with pH and dissolved oxygen control with increased oxygen supplementation was found to yield the highest cell mass concentration of 40.65 g L^-1 in 16-L stirred tank bioreactor cultivations. The cultivation in a 150-L stirred tank bioreactor revealed that oxygen is one of the most critical factors affecting cell mass production of the highly aerobic A. vinelandii. The decreased oxygen transfer rate limited cell growth but increased alginate production. The maximum cell mass obtained in a fed-batch culture of A. vinelandii in a 150-L stirred tank bioreactor was 28.35 g L^-1 while the maximum alginate concentration was 18.60 g L^-1